Liquid crystal composition, device and apparatus

ABSTRACT

A liquid crystal device showing performances, such as good viewing angle characteristic, high contrast, high-speed responsiveness, high resolution and high productivity is given by forming a layer of discotic liquid crystal placed in an edge-on and uniaxial alignment state. In the liquid crystal layer, the discotic liquid crystal may preferably assume a nematic discotic layer and co-present with a rod-shaped liquid crystal in mutually separated phases.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to a liquid crystal device for use in aflat panel display, a paper display, a projection display, a light valvefor printer, etc.; a liquid crystal composition for use in the liquidcrystal device; and a liquid crystal apparatus including the liquidcrystal device. The present invention further relates to a phasecompensation plate, a viewing angle compensation plate, a liquid crystalswitching device, an active-type liquid crystal device, and a liquidcrystal apparatus using the liquid crystal device.

CRTs (cathode ray tubes) have bee extensively used as most populardisplay devices, for motion picture display for television and videotape recorder, and monitors for personal computers. Based on theoperation characteristic, however, a CRT is accompanied withdifficulties such that the recognizability of a static picture islowered due to flicker and scanning fringes caused by an insufficientresolution, and the fluorescent screen thereof is deteriorated due toburning or sticking. Other problems of the CRT are possible adverseeffect of electromagnetic wave emitted therefrom and large powerconsumption. Further, the CRT structurally has a large rearward volumebehind the display surface, thus restricting the facility of informationapparatus including the CRT and being unsuitable for space economizationin office or home use.

As a type of device solving such problems of the CRT, there has beenknown a liquid crystal display device including a type using a twistednematic (TN)-mode liquid crystal as disclosed by M. Schadt and W.Helfrich, “Applied Physics Letters”, Vol. 18, No. 4 (Feb. 15, 1971), pp.127-128. There are also known other liquid crystal device modes,inclusive of in-plane switching mode (IPS), multi-domain verticalalignment mode (MVA), and high-speed switching modes using a smecticliquid crystal, such as ferroelectric liquid crystal (FLC) oranti-ferroelectric liquid crystal (AFLC).

In recent years, as a type of liquid crystal device, TFT-liquid crystaldevices have been developed and commercialized. The TFT-liquid crystaldevice includes a matrix of pixels each provided with a TFT (thin-filmtransistor) for solving the problem of crosstalk and is produced indisplay sizes of 10-13 inches at a good productivity owing to a rapidprogress in production technology. However, the TFT-liquid crystaldevice has left problems in production of a larger size panel with agood viewing angle characteristic and in response speed for allowing aframe frequency of 60 Hz or higher desired for satisfactory motionpicture reproduction.

These technical problems involved in liquid crystal devices areattributable to viscoelasticities and optical birefringencecharacteristic of known liquid crystal materials, and there areincessant desires for novel liquid crystal materials, and alignmentstates thereof, and novel switching modes of liquid crystal devices.

As another problem to be considered, the above-mentioned conventionalliquid crystal devices are ordinarily used as a display panel incombination with a backlight (device) by optically modulating atransmitted light passing through the liquid crystal device.Accordingly, the backlight for the liquid crystal device is required toemit a strong light. Further, a consumption power of liquid crystaldisplay apparatus is largely occupied by the backlight. Even when alithium ion-secondary battery is used for such a liquid crystal displayapparatus, a continuous (successive) operation time for, e.g., mobilecomputing is approximately several hours at the best. Thus, if backlightdevices for various liquid crystal devices can be omitted, low powerconsumption for many information equipment and office equipment isrealized, thus leading to suppression of global warming and aterrestrial environment protection.

In the circumstances, a low power consumption-type reflection liquidcrystal device without using a backlight has been developed but stillleaves room for improvement in its characteristics at present. Further,various products using a projection-type liquid crystal device as aprojector have been commercially available from electrical equipmentmanufacturers as a large picture-size display. In the field of such aliquid crystal projector, however, a further improvement in brightness(luminance) and/or contrast is required. In order to provide ahigh-brightness liquid crystal device without using a polarizer, lightscattering-type liquid crystal devices, such as one of apolymer-dispersed type and one of a polymer network-type have beendeveloped and proposed (e.g., “'93 Eurodisplay”, p. 397-). However,these liquid crystal devices are still desired to improve drivingcharacteristics, scattering performance and other characteristics.

SUMMARY OF THE INVENTION

In view of the above-mentioned state of the art, an object of thepresent invention is to provide a liquid crystal device showing a goodviewing angle characteristic, a high contrast and a high resolution at ahigh productivity.

Another object of the present invention is to provide a liquid crystaldevice capable of exhibiting high performances, such as a high luminanceand a low power consumption.

Another object of the present invention is to provide an opticalmodulation device, a display device and a liquid crystal apparatus usingsuch a liquid crystal device.

A further object of the present invention is to provide a liquid crystalcomposition suitably used as a functional material in such a liquidcrystal device.

According to the present invention, there is provided a liquid crystaldevice comprising: a layer of discotic liquid crystal placed in anedge-on and uniaxial alignment state.

According to another aspect of the present invention, there is provideda liquid crystal composition comprising: a discotic liquid crystal and arod-shaped liquid crystal disposed in mutually separate phases, whereinthe discotic liquid crystal is in a nematic discotic phase.

The present invention further provides a liquid crystal device,including a liquid crystal layer comprising a discotic liquid crystaland a rod-shaped liquid crystal disposed in mutually separate phases,wherein the discotic liquid crystal is in a nematic discotic phase.

The present invention further provides a liquid crystal apparatusincluding a liquid crystal device as described above.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are a schematic front sectional view and a schematicside sectional view respectively, of discotic liquid crystal moleculesarranged in an edge-on and uniaxial alignment state.

FIG. 2 is a schematic sectional view of an embodiment of the liquidcrystal device according to the invention.

FIG. 3 is a schematic sectional view illustrating an alignment state ofrod-shaped liquid crystal molecules.

FIG. 4 is a schematic perspective view showing an optical relationshipof refractive index ellipsoids of a polymeric discotic liquid crystal(upper) and a rod-shaped liquid crystal (lower) relative to polarizerpositions.

FIG. 5 is a schematic sectional view of an active matrix liquid crystaldevice.

FIG. 6 is a block circuit diagram illustrating an active matrix liquidcrystal device.

FIG. 7 is a schematic sectional view of another embodiment of the liquidcrystal device according to the invention.

FIGS. 8A-8B are a schematic perspective view from above and a schematicside sectional view, respectively, illustrating director alignments of arod-shaped (nematic) liquid crystal and a discotic liquid crystal.

FIG. 9 is a schematic arrangement view for illustrating a projectionoptical system including a transmission-type liquid crystal device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

As a result of my study, it has been found that a liquid crystal deviceincluding discotic liquid crystal molecules aligned in an edge-on anduniaxially aligned state is effective as a viewing angle compensatorfilm for improving the viewing angle characteristic of a nematic liquidcrystal device, etc., and provides by itself a wide-viewing angle liquidcrystal device capable of switching.

As for alignment states of discotic liquid crystals, it is well knownthat a discotic liquid crystal is aligned in a side-on alignment statewherein disks of discotic liquid crystal molecules are aligned parallelto the substrates. A hydride alignment state is also known as disclosedin JP-A 9-211444. In addition to the above, there is also known analignment state called an edge-on alignment state wherein disks ofdiscotic liquid crystal molecules stand vertically with respect to thesubstrates (as diclosed by G. Kruck, et al., Liquid Crystals, Vol. 14,No. 3, pp. 807-819). The edge-on alignment state can be ordinarilyobtained by forming a homeotropic alignment film on the substrates, butit has not been practiced to uniformly and uniaxially control thedirection of disk faces, i.e., the discotic director. This is presumablybecause of a technical difficulty of satisfying in combination anedge-on alignment generally attained by weakening the interaction with aboundary and a uniaxial alignment generally attained by strengtheningthe interaction with a boundary with respect to a discotic liquidcrystal of which the alignment is generally more difficult than arod-shaped liquid crystal.

As a result of my study regarding liquid crystal materials, alignmentfilm materials and preparation conditions, it has become possible torealize an edge-on and uniaxial alignment state of a discotic liquidcrystal. FIGS. 1A an 1B are sectional views illustrating an edge-on anduniaxially aligned state of discotic liquid crystal molecules as viewedfrom a front (FIG. 1A) and a side (FIG. 1B), respectively, of disks 10of the discotic liquid crystal molecules between a pair of boundaries 2a and 2 b (generally given by a pair of substrates, which can be removedthereafter if the alignment state is fixed, e.g., by polymerization aswill be described hereinafter). As is understood from FIGS. 1A and 1B,in the edge-on and uniaxial alignment state, the discotic liquid crystalmolecules are aligned so that their disk faces stand vertically (atleast over a substantial thickness portion) with respect to theboundaries and are directed in one direction parallel to the boundaries.

The discotic liquid crystal used in the present invention may forexample have a discotic columnar or a nematic discotic phase, but thenematic discotic phase is preferred because of a relatively highfluidity and easiness of alignment control. More specifically, thediscotic liquid crystal may for example comprise a compound having astructure as listed below (wherein specific groups denoted by symbols a,b, c, . . . are indicated after the list) or a composition containingsuch a compound.

In (D-1) to (D-9), a to k for each R are groups shown below.

Polymeric discotic liquid crystal compounds as shown below can also beused.

The discotic liquid crystal materials can further contain an ultravioletabsorber, a radical trapping agent, an antioxidant, a viscosity-loweringagent, a nematic liquid crystal, a smectic liquid crystal, etc.

The discotic liquid crystal is aligned in the liquid crystal device ofthe present invention in a manner as described below.

FIG. 2 is a schematic sectional view of a liquid crystal device formedaccording to the present invention. Referring to FIG. 1, the liquidcrystal device includes a liquid crystal layer 1 comprising a discoticliquid crystal composition disposed between a pair of substrates 2 a and2 b, which may for example comprise glass or a plastic material, and aresuccessively coated with transparent electrodes 3 a and 3 b of, e.g.,ITO, etc., and alignment control layers 4 a and 4 b. One of thealignment control layers 4 a and 4 b can be omitted, but at least one ofthe substrates 2 a and 2 b is required to have such an alignment controllayer 4 a and/or 4 b having an edge-on and uniaxial alignmentcharacteristic. Such an alignment control film having an edge-on anduniaxial alignment characteristic may be formed by vapor deposition orsputtering on a substrate from an oblique direction of an inorganicmaterial, such as silicon monoxide, silicon dioxide, aluminum oxide,zirconia, magnesium fluoride, cerium oxide, cerium fluoride, siliconnitride, silicon carbide or boron nitride; or surface rubbing with afibrous material, such as velvet cloth or paper, of a film of an organicmaterial, such as polyvinyl alcohol, polyimide, polyamideimide,polyester, polyamide, polyester imide, polyparaxylylene, polycarbonate,polyvinyl acetal, polyvinyl chloride, polystyrene, polysiloxane,cellulosic resin, melamine resin, urea resin or acrylic resin.

In order to provide a better edge-on and uniaxial alignment, it isparticularly preferred to use a rubbed polyimide layer. Such a polyimidealignment film may ordinarily be obtained by forming a film of asolvent-soluble polyamic acid, followed by baking for polyimide filmformation. It is also possible to use a solvent-soluble polyimideshowing a good voltage retentivity. Such a polyimide is preferred inview of good uniaxial alignment characteristic and high productivity. Itis further preferred to use a type of polyimide film showing ahomeotropic alignment characteristic with respect to ordinary rod-shapedliquid crystals when not subjected to rubbing and use such a polyimidefilm after a relatively intense rubbing. Such a polyimide film having ahomeotropic alignment characteristic is generally given by polyimideshaving a weakly polar structure, as represented by those having sidechains including a long-chain alkyl group, or side chains including afluorine atom or a perfluoroalkyl group.

The liquid crystal device may further comprise a sealing member 5 formedof, e.g., an epoxy adhesive (such as “STRUCTBOND” available from MitsuiKagaku K. K.) and also a spacer (not shown) usually disposed in theliquid crystal layer 1 for controlling a cell gap between the substrates2 a. The liquid crystal device can be further provided with one or morepolarizers 8 which may be disposed in, e.g., a right-angle cross nicolrelationship, and may be drive while being illuminated with incidentlight I₀ from a backlight source 6 to provide a transmitted modulatedlight I.

The liquid crystal device of the present invention including a discoticliquid crystal placed in an edge-on and uniaxial alignmentcharacteristic as shown in FIGS. 1A and 1B may for example be used as aphase-compensation plate and a viewing angle-compensation plate. Morespecifically, a discotic liquid crystal placed in an edge-on anduniaxial alignment state as shown in FIGS. 1A and 1B exhibits arefractive index anisotropy which is complementary to an alignment stateof rod-shaped liquid crystal molecules 11 as shown in FIG. 3, thusproviding a liquid crystal display device of a very excellentwide-viewing angle characteristic. It especially exhibits a particularlyexcellent matching of complementary relationship with a rod-shapedliquid crystal device of inplane-switching type, examples of which mayinclude: the so-called IPS device and FFS device using nematic liquidcrystals, and (anti-)ferroelectric liquid crystal (FLC and AFLC) devicesusing smectic liquid crystals, inclusive of passive devices and activedevices.

FIG. 4 illustrates an arrangement of such a liquid crystal deviceprovided with a phase compensator. More specifically, referring to FIG.4, a rod-shaped liquid crystal device is disposed at a lower part asrepresented by a pair of cross nicol polarizers 12 a and 12 b and arod-shaped liquid crystal represented by a refractive index ellipsoid14, and a phase compensator a viewing angle compensator disposed abovethe rod-shaped liquid crystal device and comprising a discotic liquidcrystal represented by a refractive index ellipsoid 13, the discoticliquid crystal may preferably comprise a polymeric one in order toexhibit a good durability and environmental stability. Such a polymericliquid crystal may preferably be formed by forming an edge-on anduniaxial alignment state as shown in FIGS. 1A and 1B of a polymerizablediscotic liquid crystal, followed by photopolymerization thereof forfixing the alignment state. It is also possible to use a polymericdiscotic liquid crystal in a controlled alignment state.

The discotic liquid crystal device of the present invention can also beused as a liquid crystal device including the discotic liquid crystal asa switching liquid crystal element. The switching may be effected fromthe edge-on and uniaxial alignment state as one stable state to aside-on alignment state or to an edge-on and non-axial alignment state,or between different phases of edge-on uniaxial alignment states. Theswitching may be caused by an electric field application for causing adielectric anisotropy torque change which can be detected by one or morepolarizers. As for an electric field responsiveness of a discotic liquidcrystal, a discotic liquid crystal having a negative dielectricanisotropy exhibits a more vertical disk alignment state (with itsdirector more parallel) with respect to the substrates at a largerelectric field intensity, and a discotic liquid crystal having apositive dielectric anisotropy exhibits an opposite direction ofalignment state change. It is also possible to add a nematic liquidcrystal or a smectic liquid crystal in order to enhance the dielectricanisotropy. The discotic liquid crystal device of this type can exhibita higher-speed responsiveness and a broader viewing angle characteristicthan a conventional liquid crystal device, thus providing an excellentliquid crystal switching device.

The liquid crystal device of the present invention utilizing a specificalignment state of discotic liquid crystal can also be used in othermodes of switching liquid crystal devices.

The liquid crystal device of the present invention can also be usedtogether with an active (switching) element. For example, it is possibleto form an active matrix-type liquid crystal device as shown in FIGS. 5and 6 provided with an active element to a matrix of pixels each ofwhich has an organization as described with reference to FIG. 2.Referring to FIG. 5, of transparent substrates (e.g., glass plates) 41and 42 disposed in an opposite pair, a lower substrate 41 is providedwith a plurality of transparent pixel electrodes 43 and a plurality ofactive (switching) elements 44 connected with the pixel electrodes,respectively, arranged in a matrix form. Each of the active elements 44may be formed of, e.g., a thin film transistor (TFT). The TFT maycomprise a semiconductor of an amorphous silicon-type, a polycrystallinesilicon-type, a microcrystalline-type or a single crystallinesilicon-type. As shown in FIG. 5, on the TFTs 44 and the pixelelectrodes 43, an alignment control layer 18 is formed. On the othersubstrate 42, a transparent electrode 47 and an alignment control layer19 are formed. Between the pair of substrates 41 and 42, a liquidcrystal layer 21 is disposed together with a spacer 22 and a sealingagent 20. Each of the TFTs 44 comprises a gate electrode formed on thesubstrate 41, a gate insulating film formed on the gate electrode, asemiconductor layer formed on the gate insulating film, and a sourceelectrode and a drain electrode formed on the semiconductor layer.

As shown in FIG. 6, on the (lower) substrate 41, gate (scanning) lines45 and data signal lines 46 are disposed between the pixel electrodes 43in a row direction and a column direction, respectively. Each of thesource electrodes is connected with a corresponding gate line 45 and acorresponding data signal line 46, respectively. The gate lines 45 areconnected to a row driver 31 via their terminal portions 45 a and thedata signal lines 46 are connected to a column driver 32 via theirterminal portions 46 a. The gate lines 45 are scanned by application ofgate signals from the row driver 31 and the column driver 32 suppliessignals corresponding to display data. The gate lines 45 are coveredwith the gate insulating film of the TFT 44 except for their terminalportions 45 a and the data signal lines are formed on the gateinsulating film. The pixel electrodes 43 are also formed on the gateinsulating film and are connected with corresponding drain electrodes ofthe TFTs 44, respectively, at their terminal portions. On the (upper)substrate 42, as shown in FIG. 5, the transparent (counter) electrode 47is formed so as to be counter to the respective pixel electrodes 43. Theopposite electrode 47 is a single electrode extending over the entiredisplay region and supplies a reference voltage.

When the liquid crystal device is driven, a resultant transmittance ischanged depending on the data signal voltage to effect gradationaldisplay. Each of the pixels may frequently be provided with a capacitorfor providing an auxiliary (storage) capacitance.

Such a matrix device can be used either a transmission type or areflection type. The transmission-type device ordinarily includes abacklight source (like the one denoted by numeral 6 in FIG. 2). Thereflection-type device is provided with a reflection layer included inthe device The liquid crystal device may be used either a directviewing-type or a projection type, and can also be used as a light valvefor a printer, etc.

Thus, the liquid crystal device of the present invention can be used forconstituting various liquid crystal apparatus including as arepresentative example a display apparatus including the liquid crystaldevice as a display panel, and also a drive circuit, a backlight, alight diffusion plate, etc.

Some specific examples and comparative examples are described belowregarding this embodiment of the liquid crystal device according to thepresent invention.

EXAMPLE 1-1

A polymerizable discotic liquid crystal mixture (A) comprising threecomponents each represented by the following formula (A) was prepared.

More specifically, the discotic liquid crystal mixture (A) was obtainedby mixing a component a1 (having a R₁/R₂ mol ratio of 5/1), a componenta2 (R₁/R₂=4/2) and a component a3 (R₁/R₃=3/3) in weight ratios of22:59:16. The liquid crystal mixture (A) exhibited a phase transitionseries of discotic rectangular phase (Dr)—(131° C.)—nematic discoticphase (Nd)—(200° C.)—isotropic phase (Iso) on temperature increase

(Blank cell α)

A blank cell a was prepared in the following manner.

Two 1.1 mm-thick glass substrates each coated with a ca. 70 nm-thick ITOtransparent electrode were provided.

Each glass substrate was spin-coated twice with a 4 wt. % solution of apolyimide precursor having a homeotropic alignment characteristic (“JALS2022”, made by Nippon Gosei Gomu K. K.) at 500 rpm for 5 sec (for firstcoating) and at 1500 rpm for 30 sec (for second coating).

The coating was then pre-dried at 80° C. for 2 min and baked at 200° C.for 1 hour to form a 450 Å-thick polyimide film, which was then rubbedin one direction with a 80 mm-dia. rubbing roller surfaced with cottonunwoven cloth at 1000 rpm and a cotton pressing depth of 1.2 mm whilebeing fed at a rate of 10 mm/s.

On one of the two glass substrates thus treated, a dispersion of resinbeads having an average particle diameter of 10 μm at 0.01 wt. % inisopropyl alcohol (IPA) was applied by spin coating at 1500 rpm for 10sec to disperse the spacer beads at a density of ca. 100 beads/mm², anda thermosetting adhesive was applied in a frame shape by printing.

Then, the other treated glass substrate was applied to the above-treatedone glass substrate so that the rubbing directions were parallel andidentical to each other, and the applied body was heated for 90 min. inan oven at 150° C. to cure the adhesive, thereby forming a blank cell α.

(Blank cells α′ and α″)

Blank cells α′ and α″ were respectively prepared in the same manner asabove except for using a 1 wt. % solution and a 2.3 wt. % solution,respectively, of the polyimide precursor to form polyimide alignmentfilms in thickness of 170 Å and 330 Å, respectively.

(Device α1)

The above-prepared discotic liquid crystal mixture (A) was injected at210° C. (in isotropic phase) into the above-prepared blank cell a toprepare a liquid crystal device α1. The liquid crystal device α1 wasobserved through a polarizing microscope while gradually cooling thedevice from 210° C. at a rate of 2° C./min. As a result, at 150° C., auniform alignment state exhibiting a strong uniaxial birefringence wasobserved, whereby a uniform edge-on and uniaxial alignment state wasconfirmed.

(Devices α1′ and α1″)

Device α1′ and α1″ were prepared and evaluated in the same manner asDevice α1 except for using Blank cells α′ and α″, respectively, insteadof Blank cell α. As a result, Device α1′ exhibited a side-on alignmentstate showing a slight uniaxial birefringence due to the rubbing.Devices α1″ exhibited a region of the same alignment state as Device α1′and also a region of different alignment state showing a strong uniaxialbirefringence together with a disclination between the regions.

On the other hand, Device α1 exhibited only the strong uniaxialbirefringence phase observed in α1″.

EXAMPLE 1-2

A liquid crystal composition B was prepared by mixing the discoticliquid crystal mixture (A) used in Example 1-1 with 25% of a nematicliquid crystal (“KN5030”, made by Chisso K. K.).

The liquid crystal composition B was injected into a blank cell aidentical to the one prepared in Example 1-1 to prepare a liquid crystaldevice α2, which was gradually cooled in the same manner as in Example1-1. As a result, from around 60° C., a transition to Nd phase (nematicdiscotic) was caused, and at 50° C., a uniform alignment stateexhibiting a strong uniaxial birefringence was observed, whereby auniform edge-on and uniaxial alignment state was confirmed.

EXAMPLE 1-3

To the liquid crystal composition B prepared in Example 1-2, 1 wt. % ofa photopolymerization initiator (“Irgacure 184”, made by Ciba-GeigyCorp.) was added to form a composition C, which was then injected ito ablank cell α identical to the one prepared in Example 1-1 and wasgradually cooled in the same manner as in Example 1-1. As a result, at aconstant temperature of 50° C. after the gradual cooling, a uniformalignment state exhibiting a strong uniaxial birefringence was observed,whereby a uniform edge-on and uniaxial alignment state was confirmedsimilarly as in Example 1-2.

In this state, the liquid crystal composition in the cell was exposed toca. 12 mW/cm² of ultraviolet rays having a central wavelength of 365 nmfor 5 min., thereby fixing the edge-on and uniaxial alignment state toprepare a liquid crystal device α3. The alignment state in the device α3was retained even at an elevated temperature of 120° C.

Separately, an FLC (ferroelectric liquid crystal) cell as an in-planeswitching liquid crystal device having bistability was prepared. A DCelectric field was applied to the FLC cell to provide a uniformlyaligned one uniform alignment state and was superposed with cross-nicolpolarizers disposed to provide a dark state. Then, a DC electric fieldof the other polarity was applied to the FLC cell to provide the otheruniform alignment state in a bright state exhibiting a maximumluminance. In this state, the FLC cell exhibited a retardation of 200 nmand a transmittance of 74% relative to the blank cell thereof superposedwith parallel-nicol polarizers. When the cell was observed whilechanging the viewing angle in the longer-axis direction of the liquidcrystal, an intense bluish tint was observed at an inclination angle of50 deg. or larger.

Then, the discotic liquid crystal device α3 was planed on theferroelectric liquid crystal cell, and the same viewing angle-changingtest was performed, whereby the bluish tint was remarkably decreased.

EXAMPLE 1-4

The liquid crystal device α2 prepared in Example 1-2 first placed in abright state under observation through a cross-nicol polarizingmicroscope and then was supplied with an AC electric field of 10 voltsand 60 Hz, whereby a dark view state was formed under observationthrough the polarizing microscope. The electrodes of the liquid crystaldevice in this state was connected via a single-crystal silicontransistor (on-resistance=50 ohm) and a ceramic capacitor of 2 nF to avoltage supply, thereby obtaining an active-type liquid crystal device.The device was supplied with a drive voltage of +6 volts by applying agate signal giving a selection period of 30 psec, whereby modulatedlight was observed from the device under observation through apolarizing microscope.

As described above, according to this embodiment of the presentinvention, it is possible to provide a liquid crystal (display) deviceshowing a high-viewing angle characteristic, a high contrast, ahigh-speed responsiveness and a high resolution at a high productivity.

Second Embodiment

According to this embodiment, there are provided a liquid crystalcomposition comprising a discotic liquid crystal and a rod-shaped liquidcrystal in mutually phase-separated states wherein the discotic liquidcrystal is placed in a nematic discotic phase, and a liquid crystaldevice using the liquid crystal composition wherein the discotic liquidcrystal is preferably placed in an edge-on and uniaxial alignment state.

Our research group has already proposed a dispersed orphase-separation-type liquid crystal device comprising a polymericdiscotic liquid crystal and a rod-shaped liquid crystal (in U.S. patentapplication Ser. No. 09/571,412; filed May 15, 2000). The presentinvention provides a liquid crystal composition allowing a higher orderof alignment control wherein the discotic liquid crystal is placed in anematic discotic phase which allows a easiest alignment control.

Thus, in the liquid crystal composition of the present invention, thediscotic liquid crystal and the rod-shaped liquid crystal are disposedin mutually separate phases, and the discotic liquid crystal is placedin a nematic discotic phase. The discotic liquid crystal used for thispurpose is preferably a discotic liquid crystal material showing anematic discotic phase by itself. The liquid crystal composition of thepresent invention can be obtained by mixing such a discotic liquidcrystal material with a rod-shaped liquid crystal material, preferably anematic liquid crystal when the rod-shaped liquid crystal phase. All thecombination comprising a discotic liquid crystal material showing anematic discotic phase and a rod-shaped liquid crystal is used as aswitching liquid crystal, in a mixing ratio providing a separate phasemixture of the nematic discotic phase and the rod-shaped liquid crystalcannot provide such a suitable mixing ratio. For this purpose, it ispreferred to use a discotic liquid crystal material showing a nematicdiscotic phase over a broader temperature range, and it is alsopreferred to use a rod-shaped nematic liquid crystal showing a nematicphase over a broader temperature range. It is also preferred to take ameasure of promoting the phase separation, e.g., use of mutuallyincompatible materials, such as a combination of a fluorine-containingnematic liquid crystal and a non-fluorine-containing discotic liquidcrystal. For providing such a phase separation state over a broadtemperature range, it is further preferred to fix the phase separationstate by polymerizing either one liquid crystal. As a result, it becomespossible to further promote the phase separation between the resultantpolymeric liquid crystal phase and the remaining liquid crystal phaseand suppress a re-dissolution between the two phases at a highertemperature, thereby retaining the prescribed phase separation stateover a broad temperature range.

In a preferred embodiment, the rod-shaped liquid crystal is used as aswitching liquid crystal and a polymeric discotic liquid crystalmaterial is used in combination therewith. For this purpose it ispreferred to use a polymerizable discotic liquid crystal material andplace it in the prescribed phase separation state, followed bypolymerization, e.g., photopolymerization, of the polymerizable discoticliquid crystal to fix the phase separation state. In this instance, apolymerization initiator, a stabilizer, etc. can be added as desired.

As the discotic liquid crystal materials, the above-mentioned examplesmaterials (D-1) to (D-20) and (PMD-1) to (PMD-4) may for example beused. It is possible to provide a polymerizable discotic liquid crystalcompound by introducing a polymerizable group to a skeleton asrepresented by (D-1) to (D-20) above. Examples of polymeric discoticliquid crystal compounds formed by polymerization of such polymerizablediscotic liquid crystal compounds include (PMD-1) to (PMD4) above.

As the rod-shaped liquid crystal, a nematic liquid crystal and a smecticliquid crystal may preferably be used, but a nematic liquid crystal isparticularly preferably used in view of a productivity, a material cost,and a switching characteristic. A large number of commercially availablenematic liquid crystals can be used for this purpose. As smectic liquidcrystals, it is possible to use an SA liquid crystal (i.e., a smecticliquid crystal having a smectic A phase), a ferroelectric liquidcrystal, an anti-ferroelectric liquid crystal or a chiral smectic liquidcrystal.

The liquid crystal composition of the present invention comprising adiscotic liquid crystal and a rod-shaped liquid crystal in a nematicdiscotic phase may be used in this state but can also be used in adifferent state, e.g., a state wherein the discotic liquid crystalplaced in a controlled alignment state in its nematic discotic phase isfurther transitioned into a higher-order discotic phase also with acontrolled alignment state in this phase.

The liquid crystal composition of the present invention may comprise 1to 99 wt. % of the discotic liquid crystal and 1 to 99 wt. % of therod-shaped liquid crystal, preferably 5 to 95 wt. % of the discoticliquid crystal and 5 to 95 wt. % of the rod-shaped liquid crystal. It isalso possible to incorporate additives, such as a polymerizationinitiator, a stabilizer, an antioxidant, a viscosity-lowering agent anda colorant, as desired.

FIG. 7 is a schematic sectional view of a liquid crystal deviceincluding a layer of such a liquid crystal composition according to thisembodiment of the present invention. More specifically, the liquidcrystal device includes a liquid crystal layer 201 comprising a polymernetwork 208 formed of a polymeric discotic liquid crystal and also arod-shaped liquid crystal 207 as an electric field-responsive liquidcrystal. Thus, by changing an electric field applied to the liquidcrystal layer 201, the alignment or orientation state of the rod-shapedliquid crystal 207 can be changed. The liquid crystal layer 201 maypreferably have a thickness selected in the range of 1 μm to 10 μm. Thethickness (cell gap) of the liquid crystal layer 201 may be controlledby, e.g., spacer beads 205 (only one being shown) disposed between apair of substrates 202 a and 202 b which are formed of, e.g., glass orplastic. The substrates 202 a and 202 b are coated with transparentelectrodes 203 a and 203 b, respectively of, e.g., ITO, and alignmentcontrol layers 204 a and 204 b, respectively, which can be omitted. Inaddition to these members, it is also possible to include a shortcircuit prevention layer, a light-absorbing layer, a reflection layer, acolor filter layer, etc., as desired. Further, in case of using theliquid crystal device as a scattering device or a reflection device, itis possible to omit one of the substrates 202 a and 202 b, or to use apair of mutually different (or asymmetrical) substrates.

In a preferred embodiment of the present invention, the discotic liquidcrystal 208 phase-separated from the rod-shaped liquid crystal 207 isplaced in an edge-on and uniaxial alignment state, e.g., by using aunidirectionally rubbed polyimide alignment film for the alignmentcontrol layers 204 a and 204 b. In this state, if the rod-shaped liquidcrystal molecule 207 a is switched to an orientation state (as shown inleft halves of FIGS. 8A and 8B) providing an alignment director (n₃)which is perpendicular to the alignment director (n_(d3)) of thediscotic liquid crystal molecule 208 a within a plane parallel to thesubstrates. This is a state giving a minimum of refractive indexdifference with respect to light falling perpendicularly to the devicesubstrates, thus providing a light transmission state. On the otherhand, if the rod-shaped liquid crystal molecule is switched to anorientation state (as shown in right halves of FIGS. 8A and 8B)providing an alignment director (n₃) which is parallel to the alignmentdirector (nd₃) of the discotic liquid crystal molecular 208 a. This is astate giving a very large refractive index differences in respectivedirections to provide a light scattering state. By using either one(together with another state) or both (together with or without anotherstate) of the above-mentioned two states, the liquid crystal device canperform a switching operation, e.g., according to reflection lightcontrol.

In order to effect the above-mentioned switching operation, it isnecessary to perform a so-called in-plane switching of the rod-shapedliquid crystal, e.g., by disposing comb-teeth-shaped electrodes capableof causing a lateral electric field or by using, e.g., a ferroelectricliquid crystal capable of causing such in-plane switching underapplication of a vertical electric field across the liquid crystal layerthickness. As briefly mentioned above, the above switching operation isillustrated in FIGS. 8A and 8B based on refractive index ellipsoids of arod-shaped liquid crystal molecule 207 a and a discotic liquid crystalmolecule 208 a.

Of the two orientation states shown in FIGS. 8A and 8B, the stateincluding mutually parallel directors (n₃ and n_(d3)) of the rod-shapedliquid crystal molecule 207 a and the discotic liquid crystal molecule208 a (shown in right halves of FIGS. 8A and 8B) is effective forproviding a strong light scattering intensity. In FIGS. 8A and 8B, theorientations of the respective liquid crystal molecules are representedby refractive index directors. More specifically, a rod-shaped liquidcrystal (molecule) have two indexes n₁ and n₂ in shorter-axis directionswhich are smaller than a refractive index n₃ in a longer-axis direction.For a nematic liquid crystal, n₁=n₂. On the other hand, a discoticliquid crystal (molecule) 208 a assumes a round and flat bread- ordisk-shaped refractive index ellipsoid including larger n_(d1) andn_(d2) and smaller n_(d3). The reason for the strong light scatteringintensity in the state of parallel directors shown in the right halvesof FIGS. 8A and 8B can be explained based on typical values ofrefractive indices in respective axial directions of a rod-shaped liquidcrystal and a discotic liquid crystal, relative to those of a matrixpolymer used in an ordinary polymer dispersion-type liquid crystaldevice, as shown in Table 1 below. TABLE 1 Refractive index in 1st 2nd3rd Material direction direction direction Rod-shaped 1.5 (n₁) 1.5 (n₂)1.7 (n₃) liquid crystal Discotic  1.7 (n_(d1))  1.7 (n_(d2))  1.5(n_(d3)) liquid crystal Ordinary 1.5 (n₁) 1.5 (n₂) 1.5 (n₃) matrixpolymer

As briefly mentioned above, the light-scattering performance of a mediumlargely depends on a difference in refractive index between componentmaterials copresent in phase separation with respect to incident light.As is understood from the data shown in Table 1 above, in an ordinarypolymer dispersion-type liquid crystal system comprising a rod-shapedliquid crystal and an ordinary polymer, a substantial refractive indexdifference (1.7 (n₃)−1.5 (n₃=0.2) is found in only the third direction.On the other hand, in the phase separation system of the presentinvention comprising a rod-shaped liquid crystal 207 a and a discoticliquid crystal 208 a placed in the parallel director orientation oralignment state shown in the right halves of FIGS. 8A and 8B, such arefractive index difference is found in all the three directions.Accordingly, intense light scattering is caused at the boundary betweenthe rod-shaped liquid crystal phase and the discotic liquid crystalphase. This has been experimentally confirmed.

In order to stably utilize the phase-separation system of a discoticliquid crystal and a rod-shaped liquid crystal over a broad temperaturerange, it is preferred to provide a so-called polymer dispersion liquidcrystal system by polymerizing either one of the discotic liquid crystaland the rod-shaped liquid crystal, preferably the discotic liquidcrystal. This can be easily achieved by photopolymerization of apolymerizable discotic liquid crystal in a state of phase-separationmixture with a rod-shaped liquid crystal as mentioned above.Alternative, it is also possible to mix a polymeric discotic liquidcrystal material with a rod-shaped liquid crystal. Examples of such apolymeric discotic liquid crystals include (PMD-1) to (PMD-4) mentionedabove. Other examples may include those described in JP-A 8-27284,“Macromol. Rapid Commun.”, Vol. 18, pp. 93-98 (1977), “EKISHO”, Vol. 1,p. 45- (1977).

A reflection light control-type liquid crystal device described abovecan be used to constitute a liquid crystal device exhibiting veryexcellent luminance without requiring a backlight which is largepower-consuming device. It is also possible to place a light-absorbingplate or a reflection plate (as described in, e.g., “IRDC”, '94, p.183-) to improve the luminance or contrast. The liquid crystal device ofreflection type may also be used as a direct viewing-type liquid crystaldisplay device using external light or a supplementary light source. Itis also possible to use the liquid crystal device in a so-calledprojection-type liquid crystal apparatus wherein light incident to andmodulated reflected light from the liquid crystal device is subjected tooptical path control to be projected onto a screen.

In such a projection-type liquid crystal apparatus, the liquid crystaldevice of the present invention can be constituted as atransmission-type device instead of a reflection-type device describedabove.

FIG. 9 illustrates a typical embodiment of the transmission-typeprojection liquid crystal apparatus using a Schlieren optical system.Referring to FIG. 9 three liquid crystal devices 303 a, 303 b and 303 cfor primary colors of R (red), G (green) and B (blue) are each comprisedof a liquid crystal device having an electrode matrix (e.g., as anactive matrix-type liquid crystal device described with reference toFIGS. 5 and 6), so that a color picture is projected and displayed ontothe screen. More specifically, an incident light issued from a lightsource 301 is selectively reflected and color-separated into lightfluxes of R, G and B by dichroic mirrors 302 a, 302 b and 302 c to enterSchlieren optical systems 304 a, 304 b and 304 c including a Schlierenlens 308 a (308 b, 308 c) and the liquid crystal device 303 a (303 b,303 c). The light fluxes passing through the Schlieren optical systemsare focused and reflected by a dichroic prism 305 to pass through aprojection lens 306, thus being projected onto the screen as a colorpicture. Each of the liquid crystal devices 303 a, 303 b and 303 c isdriven by a liquid crystal driving means 307.

The liquid crystal device of the present invention can also be used as alight valve for a printer, a copying machine, etc. The liquid crystaldevice of the present invention can also be used to constitute a liquidcrystal apparatus or liquid crystal device-loaded apparatus, such asmobile computers, plasma-addressed liquid crystal display apparatus,desktop computers, video cameras, digital cameras, and documentaryviewers.

Because of a good switching characteristic of the liquid crystal deviceof the present invention as described above, such a liquid crystalapparatus can provide a high-resolution large-area display picture at ahigh speed with excellent drive characteristic and reliability.

Now, some specific examples of this embodiment will be described.

EXAMPLE 2-1

<Polymerizable discotic liquid crystal>

The discotic liquid crystal mixture (A) used in Example 1-1 was used asa polymerizable discotic liquid crystal.

<Rod-shaped liquid crystal>

A nematic liquid crystal having a dielectric anisotropy of 0.16 and aspontaneous polarization of +8 (“KN5027” made by Chisso K. K.) was usedas a nematic liquid crystal (B). The liquid crystal (B) showed a phasetransition series of Cryst.—(−30° C.) —nematic phase (N)—81° C.—Iso ontemperature increase.

The liquid crystals (A) and (B) were mixed in a weight ratio of 50/50 toprepare Mixture liquid crystal (1).

<Blank cell β>

Two 1.1 mm-thick glass substrates were provided. Each glass substratewas provided with comb teeth-shaped ca. 70 nm-thick ITO electrodes eachin a width of 15 μm at a spacing of 50 μm so as to allow a lateralelectric field application.

Each glass substrate provided with the ITO electrodes was spin-coatedtwice with a 4 wt. % solution of a polyimide precursor (“JALS 2022”,made by Nippon Gosei K. K.) at 500 rpm for 5 sec (for first coating) andat 1500 rpm for 30 sec (for second coating). The coating was thenpre-dried at 80° C. for 5 min and baked at 200° C. for 1 hour to form apolyimide film. The coatings on the two substrates were then rubbedrespectively in one direction perpendicular to the comb teeth-shapedelectrodes on one substrate and parallel to the comb teeth-shapedelectrodes on the other substrate.

On one of the two glass substrates thus treated, a dispersion of resinbeads having an average particle diameter of 10 μm at 0.01 wt. % inisopropyl alcohol (IPA) was applied by spin coating at 1500 rpm for 10sec to disperse the spacer beads at a density of ca. 100 beads/mm², anda thermosetting adhesive was applied in a frame shape by printing.

Then, the other treated glass substrate was applied to the above-treatedone glass substrate so that the rubbing directions were parallel andidentical to each other, and the applied body was heated for 90 min. inan oven at 150° C. to cure the adhesive, thereby forming a blank cell β.As a result, in the blank cell β, the electrodes on an upper substratewere disposed to apply a lateral electric field parallel to the rubbingdirection, and the electrodes on a lower substrate were disposed toapply an electric field perpendicular to the rubbing direction.

To Mixture liquid crystal (1) prepared above, 200 ppm of2,6-di-t-butylphenol and 2 wt. % of a photopolymerization initiator(“Irgacure 184”, made by Ciba-Geigy Corp.) were added, and the resultantmixture heated in an isotropic phase was injected into theabove-prepared blank cell β under normal pressure to prepare a liquidcrystal device β1. Thereafter, the liquid crystal device β1 was cooledat a rate of 10° C./min., whereby at 20° C., phase separation into anematic discotic phase and a nematic phase was observed. This state washeld for 10 min, and as a result, the transmission of intense polarizedlight through the nematic discotic phase was observed under observationthrough a polarizing microscope, whereby a uniform edge-on and uniaxialalignment state of the nematic discotic phase was confirmed. In thisstate, the liquid crystal device β1 was exposed to ca. 12 mW/cm² ofultraviolet rays having a central wavelength of 365 nm for 5 min. topolymerize the nematic discotic phase.

As a result of observation of the device placed on a hot stage (made byMettler Instrumente A. G.), the alignment state after 10 min. of holdingand before the polymerization of the nematic discotic phase was found tobe retained over a broad range, and the texture of the discotic liquidcrystal was retained even at 200° C.

An AC electric field of 110 volts and 1 kHz was applied between theelectrodes on the lower substrate while keeping open the electrodes onthe upper substrate to align the nematic liquid crystal moleculesparallel to the substrates (an alignment state shown in the right halvesof FIGS. 8A and 8B), whereby a remarkably increased scattering state wasobserved with eyes.

COMPARATIVE EXAMPLE 2-1

A polymerizable composition was prepared in the same manner as inExample 2-1 except for using hexylene diacrylate instead of thepolymerizable discotic liquid crystal mixture (A) (i.e., a 50/50 (byweight) mixture of hexylene diacrylate and “KN-5027”, together with2,6-di-t-butylphenol and polymerization initiator).

The polymerizable composition was injected into a blank cell β identicalto the one in Example 2-1 and subjected to UV-exposure forpolymerization similarly as in Example 2-1 to prepare a polymerdispersion-type liquid crystal device β.comp.

The device β.comp was backed by a black light-absorbing plate andsubjected to measurement of a reflected light intensity at an exit lightangle of 0 deg. in response to incident light at an angle of 30 deg. byusing an automatic polarizing photometer (“GP-200”, made by K. K.Murakami Shikisai Gijusu Kenkyusho).

The same reflected light intensity measurement was also performed byusing the liquid crystal device β1 under the application of AC 110 voltsand 1 kHz obtained by Example 2-1. As a result, the liquid crystaldevice β1 exhibited a reflected light intensity which was 3.4 times thatobtained by the liquid crystal device β.comp.

EXAMPLE 2-2

The liquid crystal device β1 prepared in Example 2-1 was subjected to ACvoltage application of 110 volts and 1 kHz between the electrodes on theupper substrate while opening the electrodes on the lower substrate, anda reflected light intensity in this state was measured.

As a result, the alignment state obtained by the application of ACvoltage of 110 volts and 1 kHz to the electrodes on the upper substrate(in this Example) and the alignment state obtained by the application ofthe same voltage (obtained in Example 2-1) exhibited a reflected lightintensity ratio of 1.0:1.43, thus showing a clear contrast therebetween.

As described above, according to the present invention, there isprovided a liquid crystal device which is usable as a liquid crystaldevice, an optical modulation device and a display device exhibitinghigh luminance and high performances. By using the liquid crystal deviceshowing high luminance and high performances, liquid crystal apparatusshowing various performances can be realized.

1-13. (Cancelled)
 14. A liquid crystal composition comprising: adiscotic liquid crystal and a rod-shaped liquid crystal disposed inmutually separate phases, wherein the discotic liquid crystal is in anematic discotic phase, wherein said discotic liquid crystal comprises apolymeric discotic liquid crystal formed by polymerization of apolymerizable discotic liquid crystal compound.
 15. The liquid crystalcomposition according to claim 14, wherein said polymeric discoticliquid crystal has been formed by photopolymerization of thepolymerizable discotic liquid crystal compound. 16-20. (Cancelled)
 21. Aliquid crystal device including a liquid crystal layer comprising adiscotic liquid crystal and a rod-shaped liquid crystal disposed inmutually separate phases, wherein the discotic liquid crystal is in anematic discotic phase, wherein the liquid crystal layer is placed in analignment state where the discotic liquid crystal and the rod-shapedliquid crystal are aligned to have alignment directors which areperpendicular to each other. 22-27. (Cancelled)